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Perl 5.26 container image

This container image includes Perl 5.26 as an S2I base image for your Perl 5.26 applications. Users can choose between RHEL, CentOS and Fedora based builder images. The RHEL images are available in the Red Hat Container Catalog, the CentOS images are available on Quay.io, and the Fedora images are available in Fedora Registry. The resulting image can be run using podman.

Note: while the examples in this README are calling podman, you can replace any such calls by docker with the same arguments.

Description

Perl 5.26 available as container is a base platform for building and running various Perl 5.26 applications and frameworks. Perl is a high-level programming language with roots in C, sed, awk and shell scripting. Perl is good at handling processes and files, and is especially good at handling text. Perl's hallmarks are practicality and efficiency. While it is used to do a lot of different things, Perl's most common applications are system administration utilities and web programming.

This container image includes an cpanm utility, so users can use it to install Perl modules for their web applications. There is no guarantee for any specific CPAN module version, that is included in the image; those versions can be changed anytime.

Usage in Openshift

In this example, we will assume that you are using the ubi8/perl-526 image, available via perl:5.26 imagestream tag in Openshift. To build a simple perl-sample-app application in Openshift:

oc new-app perl:5.26~https://github.com/sclorg/dancer-ex.git

To access the application:

oc get pods
oc exec <pod> -- curl 127.0.0.1:8080

Source-to-Image framework and scripts

This image supports the Source-to-Image (S2I) strategy in OpenShift. The Source-to-Image is an OpenShift framework which makes it easy to write images that take application source code as an input, use a builder image like this Perl container image, and produce a new image that runs the assembled application as an output.

To support the Source-to-Image framework, important scripts are included in the builder image:

  • The /usr/libexec/s2i/assemble script inside the image is run to produce a new image with the application artifacts. The script takes sources of a given application and places them into appropriate directories inside the image. It utilizes some common patterns in Perl application development (see the Environment variables section below).
  • The /usr/libexec/s2i/run script is set as the default command in the resulting container image (the new image with the application artifacts). It runs httpd for production.

Building an application using a Dockerfile

Compared to the Source-to-Image strategy, using a Dockerfile is a more flexible way to build a Perl container image with an application. Use a Dockerfile when Source-to-Image is not sufficiently flexible for you or when you build the image outside of the OpenShift environment.

To use the Perl image in a Dockerfile, follow these steps:

1. Pull a base builder image to build on

podman pull ubi8/perl-526

An RHEL8 image ubi8/perl-526 is used in this example.

2. Pull and application code

An example application available at https://github.com/sclorg/dancer-ex.git is used here. Feel free to clone the repository for further experiments.

git clone https://github.com/sclorg/dancer-ex.git app-src

3. Prepare an application inside a container

This step usually consists of at least these parts:

  • putting the application source into the container
  • installing the dependencies
  • setting the default command in the resulting image

For all these three parts, users can either setup all manually and use commands perl and cpanm explicitly in the Dockerfile (3.1.), or users can use the Source-to-Image scripts inside the image (3.2.; see more about these scripts in the section "Source-to-Image framework and scripts" above), that already know how to set-up and run some common Perl applications.

3.1 To use your own setup, create a Dockerfile with this content:
FROM ubi8/perl-526

# Add application sources
ADD app-src .

# Install the dependencies
RUN cpanm --notest -l extlib Module::CoreList && \
    cpanm --notest -l extlib --installdeps .

RUN printf '\
<Location />\n\
SetHandler perl-script\n\
PerlResponseHandler Plack::Handler::Apache2\n\
PerlSetVar psgi_app app.psgi\n\
</Location>\n' > /opt/app-root/etc/httpd.d/40-psgi.conf

# Run scripts uses standard ways to run the application
CMD exec httpd -C 'Include /opt/app-root/etc/httpd.conf' -D FOREGROUND
3.2 To use the Source-to-Image scripts and build an image using a Dockerfile, create a Dockerfile with this content:
FROM ubi8/perl-526

# Add application sources to a directory that the assemble scriptexpects them
# and set permissions so that the container runs without root access
USER 0
ADD app-src /tmp/src
RUN chown -R 1001:0 /tmp/src
USER 1001

# Install the dependencies
RUN /usr/libexec/s2i/assemble

# Set the default command for the resulting image
CMD /usr/libexec/s2i/run

4. Build a new image from a Dockerfile prepared in the previous step

podman build -t perl-app .

5. Run the resulting image with final application

podman run -d perl-app

Environment variables for Source-to-Image

To set environment variables, you can place them as a key value pair into a .s2i/environment file inside your source code repository.

  • ENABLE_CPAN_TEST

    Allow the installation of all specified cpan packages and the running of their tests. The default value is false.

  • CPAN_MIRROR

    This variable specifies a mirror URL which will used by cpanminus to install dependencies. By default the URL is not specified.

  • PERL_APACHE2_RELOAD

    Set this to "true" to enable automatic reloading of modified Perl modules.

  • HTTPD_START_SERVERS

    The StartServers directive sets the number of child server processes created on startup. Default is 8.

  • HTTPD_MAX_REQUEST_WORKERS

    Number of simultaneous requests that will be handled by Apache. The default is 256, but it will be automatically lowered if memory is limited.

  • PSGI_FILE

    Override PSGI application detection.

    If the PSGI_FILE variable is set to empty value, no PSGI application will be detected and mod_perl not be reconfigured.

    If the PSGI_FILE variable is set and non-empty, it will define path to the PSGI application file. No detection will be used.

    If the PSGI_FILE variable does not exist, autodetection will be used: If exactly one ./*.psgi file exists, mod_perl will be configured to execute that file.

  • PSGI_URI_PATH

    This variable overrides location URI path that is handled path the PSGI application. Default value is "/".

See also

Dockerfile and other sources are available on https://github.com/sclorg/s2i-perl-container. In that repository you also can find another versions of Perl environment Dockerfiles. Dockerfile for CentOS is called Dockerfile, Dockerfile for RHEL7 is called Dockerfile.rhel7, for RHEL8 Dockerfile.rhel8 and the Fedora Dockerfile is called Dockerfile.fedora.